These patients are most often young men (average age 16 to 17.5 years) who present complaining of the sudden onset of pain in one testicle. The pain is then followed by swelling of the affected testicle, reddening of the overlying scrotal skin, lower abdominal pain, nausea, and vomiting. An examination reveals a swollen, tender, retracted testicle that often lies in the horizontal plane (bell-clapper deformity). The spermatic cord is frequently swollen on the affected side. In delayed presentations, the entire hemiscrotum may be swollen, tender, and firm. The urine is usually clear with a normal urinalysis. In one-third of cases there is a peripheral leukocytosis.